NAME

       rtf_create_chebychev,  rtf_create_butterworth  -  Creates  IIR  Chebychev  and  Butterwoth
       filters

SYNOPSIS

       #include <rtf_common.h>

       hfilter rtf_create_chebychev(unsigned int nchann, int proctype,
                                    double fc, unsigned int num_pole,
                                    int highpass, double r);
       hfilter rtf_create_butterworth(unsigned int nchann, int proctype,
                                      double fc, unsigned int num_pole,
                                      int highpass);

DESCRIPTION

       rtf_create_chebychev() creates a IIR chebychev filter processing nchann channels  of  data
       type  specified  by proctype with fc as normalized cutoff frequency, whose the Z-transform
       has num_pole poles and whose the impulse response  has  a  ripple  of  r  This  latter  is
       expressed  as  the  ratio  between  the overshoot (difference between the max value of the
       response to a unit step and the unit length) and the unit length (ratio not  expressed  in
       decibels).

       rtf_create_butterworth()  is  the same as rtf_create_chebychev() but creates a butterworth
       filter (which a special case of a chebychev filter with a ripple of 0).

       A normalized frequency is the ratio  between  the  absolute  frequency  and  the  sampling
       frequency (i.e. a value of 1.0 refers to the sampling frequency).

       If  highpass  is  0, it specifies the filter should be a lowpass. If highpass is non-zero,
       the should be a highpass.

RETURN VALUE

       Returns the handle to the created filter in case of success, NULL otherwise.

SEE ALSO

       rtf_create_filter(3), rtf_destroy_filter(3)